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Publication numberUS6879130 B2
Publication typeGrant
Application numberUS 10/715,857
Publication dateApr 12, 2005
Filing dateNov 19, 2003
Priority dateNov 20, 2002
Fee statusPaid
Also published asEP1422820A1, US20040135539
Publication number10715857, 715857, US 6879130 B2, US 6879130B2, US-B2-6879130, US6879130 B2, US6879130B2
InventorsYasusuke Iwashita, Takahiro Akiyama, Junichi Tezuka
Original AssigneeFanuc Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Controller for induction motor
US 6879130 B2
Abstract
A controller for a vector control of an induction motor, which is capable of easily determining a rotor resistance for use in calculation of a slip frequency. A temperature sensor is provided for detecting a temperature of a stator. Information on relation between the rotor temperature and the rotor resistance predetermined based on measurement is stored in a table. In driving the induction motor, the rotor resistance for the stator temperature detected by the temperature sensor is read from the table. A torque command I2 is divided by a magnetic flux command Φ2 and the obtained quotient is multiplied by the read value of the rotor resistance to obtain the slip frequency ωs, so that the vector control is performed based on the obtained slip frequency ωs. The value of the rotor resistance is easily determined by simply referring the table without complicated calculation. Since the stored information on the rotor resistance are based on measured values, a more precise value of the slip frequency is obtained to realize a precise vector control of the induction motor.
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Claims(1)
1. A controller for performing a vector control of an induction motor having a stator and a rotor using a rotor resistance, comprising:
a temperature sensor for detecting a stator temperature;
a table storing information on relation between the stator temperature and the rotor resistance predetermined based on measurement; and
a processor to obtain a value of the rotor resistance for the stator temperature detected by said temperature sensor referring said table, and to calculate a slip frequency for the vector control based on the obtained value of the rotor resistance.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a controller for performing a vector control of an induction motor.

2. Description of Related Art

There is known a method of performing a vector control of an induction motor using a rotor resistance of the induction motor. However, it is necessary to perform temperature compensation on the rotor resistance since the rotor resistance varies with the temperature. It is difficult to directly detect an actual rotor resistance or the rotor temperature in operating the motor. Thus, in order to determine the rotor resistance, there has been proposed a method of estimating the rotor temperature based on a present value or historical values of a torque current of the motor and a predetermined thermal constant such as a thermal time constant, so that the rotor resistance is determined based on the estimated rotor temperature (e.g. JP 7-67400A).

Further, there has been proposed a method of determining the rotor temperature based on a detected stator temperature, a heat conduction amount estimated using heat conduction models of the stator and the rotor, and a heat loss of the rotor, so that the rotor resistance is determined based on the rotor temperature (e.g. JP 10-23799A). Further, there is known a method of calculating the rotor temperature based on detected temperatures of the stator and ambience thereof to compensate a slip frequency based on the calculated rotor temperature (e.g. JP 1-174286A).

Moreover, there is known a method of determining a temperature compensation amount based on a detected stator temperature and a reference temperature thereof, and calculating the rotor resistance after temperature compensation based on the determined temperature compensation amount and a rotor resistance at the reference temperature, so that the slip frequency is obtained based on the calculated rotor resistance (e.g. JP 2707680B).

In the above conventional vector control of the induction motor, the rotor resistance is obtained by calculation using estimated values or models. Thus, the processing for obtaining the slip frequency is complicated since the rotor resistance is obtained by the calculation.

SUMMARY OF THE INVENTION

The present invention provides a controller for vector controlling a induction motor capable of determining a rotor resistance easily to obtain a slip frequency.

A controller of an induction motor of the present invention comprises: a temperature sensor for detecting a stator temperature; a table storing relation between the stator temperature and the rotor resistance measured in advance; and a processor to obtain a value of the rotor resistance for the stator temperature detected by the temperature sensor referring to the table, and determine a slip frequency based on the obtained value of the rotor resistance for use in the vector control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a controller for vector controlling an induction motor according to an embodiment of the present invention;

FIG. 2 is a detailed block diagram of a slip computation section in the controller as shown in FIG. 1;

FIG. 3 is a graph of measured values of the rotor resistance with respect to a stator temperature to be stored in a table; and

FIG. 4 is a flowchart of processing of computation of a slip frequency to be performed by a processor of the controller.

DETAILED DESCRIPTION

As shown in FIG. 1, a velocity of an induction motor 7 detected by a velocity detector 8 provided at the induction motor 7 is subtracted from a velocity command issued from a host numerical controller to obtain a velocity deviation. A velocity control section 1 obtains a torque command (rotor current command) I2 by performing PI (proportional plus integral) control. A slip frequency calculating section 4 receives the torque command I2, a magnetic flux (rotor magnetic flux) command Φ2 determined in accordance with a rotational velocity of the motor 7, and a temperature T detected by a temperature sensor 9 provided at a stator of the motor 7 and performs the processing as described later to obtain a slip frequency ωs. The velocity of the motor is added to the slip frequency ωs to obtain an excitation frequency and the obtained excitation frequency is outputted to a current control section 2.

The excitation frequency is integrated by an integrator 6 to obtain a phase. The current conversion processing section 5 performs a d-q conversion based on driving currents of three phases detected by current detectors 10 u, 10 v, 10 w, respectively, and the phase obtained by the integrator 6, to obtain a torque current of a q-phase.

The torque current obtained by the current conversion processing section 5 is subtracted from the torque current command I2 outputted from the velocity control section 1 to obtain a current deviation to be inputted to the current control section 2. The current control section 2 performs a vector control based on the inputted current deviation, the excitation frequency and the excitation current command (not shown), to obtain a voltage command and converts the obtained voltage command into three-phase voltages to be outputted to an inverter 3 so as to drivingly control the induction motor 7.

The above hardware configuration of the controller is easily achieved by providing a general controller for performing a vector control of an induction motor with the temperature sensor 9 for detecting the rotor temperature of the induction motor 7 so that an output thereof is inputted to the slip frequency calculation section 4.

A detailed block diagram of the slip frequency calculation section 4 is shown in FIG. 2. The slip frequency calculation section 4 comprises a divider 41, a multiplier 42 and a table 43 storing information on values of the rotor resistance for the stator temperature. The torque current command (rotor current command) I2 is divided by a commanded magnetic flux Φ2 and the obtained quotient is multiplied by the value of the rotor resistance R2 read from the table 43 for the present stator temperature T at the multiplier 42, to output the slip frequency ωs. Thus, the calculation according to the following equation (1) is performed to obtain the slip frequency ωs.
ωs=(I 22)R 2  (1)

The table 43 stores values of the rotor resistance value R2 for the stator temperature T detected by the temperature sensor 9 based on measurements in performing operations of the induction motor 7. FIG. 3 is a graph showing relation between the stator temperature T and the rotor resistance R2 based on the measurements, and information on values of the rotor resistance R2 with respect to the stator temperature T are stored in the table 43.

Since a value of the rotor resistance R2 for the present stator temperature T detected by the temperature sensor 9 is read from the table 43, the value of the rotor resistance R2 is easily obtained to determine the slip frequency ω s.

The above processing can be performed by a dedicated circuitry but is preferably performed by a processor of the controller as software processing. The processing for calculating the slip frequency to be performed by the processor in the controller is shown in FIG. 4.

First, the torque current 12 obtained by the velocity control processing is read (Step 100), and the magnetic flux command Φ2 is read (Step 101). The stator temperature T detected by the temperature sensor 9 is read (Step 102) and the value of the rotor resistance R2 for the read stator temperature T is read from the table 43 (Step 103). The calculation according to the equation (1) using the torque current I2, the magnetic flux command Φ2, and the rotor resistance R2 is performed to obtain the slip frequency (Step 104) and the obtained slip frequency is issued for other processing, to terminate the procedure.

According to the present invention, the rotor resistance is easily obtained based on the detected stator temperature so that the slip frequency is easily and quickly determined. Since the values of the rotor resistance are predetermined based on actual measurements, the slip frequency is precisely determined to enable a precise vector control of the induction motor.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4441065 *Aug 13, 1981Apr 3, 1984Siemens AgMethod and apparatus for determining the rotor resistance of an asynchronous machine
US4450398Apr 5, 1982May 22, 1984General Electric CompanyMicroprocessor-based efficiency optimization control for an induction motor drive system
US4567419 *Jul 3, 1984Jan 28, 1986Mitsubishi Denki Kabushiki KaishaControl apparatus for elevator
US4672288 *Jun 18, 1985Jun 9, 1987Westinghouse Electric Corp.Torque controller for an AC motor drive and AC motor drive embodying the same
US4926105 *Feb 17, 1987May 15, 1990Mischenko Vladislav AMethod of induction motor control and electric drive realizing this method
US5294876Aug 2, 1991Mar 15, 1994Joensson RagnarMethod and apparatus for controlling an AC induction motor by indirect measurement of the air-gap voltage
US5476158 *Mar 31, 1993Dec 19, 1995Otis Elevator CompanyRotor time constant adaptation for induction motor in vector controlled elevator drive
US6075337 *May 11, 1999Jun 13, 2000Fuji Electric Co., Ltd.Speed control apparatus for induction motor
JPH0767400A Title not available
JPH1023799A Title not available
JPH01174286A Title not available
JPH02211087A Title not available
Non-Patent Citations
Reference
1Patent Abstracts of Japan of JP 01023799 dated Jan. 26, 1989.
2Patent Abstracts of Japan of JP 01174286 dated Jul. 10, 1989.
3Patent Abstracts of Japan of JP 07067400 dated Mar. 10, 1995.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7423401 *Dec 28, 2004Sep 9, 2008Mitsubishi Denki Kabushiki KaishaAC rotary machine constant measuring apparatus for measuring constants of stationary AC rotary machine
US7511449Oct 31, 2006Mar 31, 2009Caterpillar Inc.Electric motor system implementing vector and slip control
US7560895Mar 16, 2007Jul 14, 2009Azure Dynamics, Inc.Indirect rotor resistance estimation system and method
US20050062450 *Aug 13, 2004Mar 24, 2005Gary PaceRotor resistance estimation by calibrated measurement of stator temperature
US20070224074 *Mar 27, 2007Sep 27, 2007Daido Metal Company Ltd.Method of manufacturing a clad material of bronze alloy and steel
US20080018284 *Dec 28, 2004Jan 24, 2008Mitsubishi Elect. Build. Techno-Serv. Co., Ltd.Ac Rotary Machine Constant Measuring Apparatus For Measuring Constants Of Stationary Ac Rotary Machine
US20080100257 *Oct 31, 2006May 1, 2008Speckhart Gregory JElectric motor system implementing vector and slip control
Classifications
U.S. Classification318/807, 318/803, 318/811, 318/813, 318/727
International ClassificationH02P21/00, H02P27/04, H02P21/08
Cooperative ClassificationH02P21/10, H02P21/09
European ClassificationH02P21/08S, H02P21/10
Legal Events
DateCodeEventDescription
Nov 19, 2003ASAssignment
Owner name: FANUC LTD., JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:IWASHITA, YASUSUKE;AKIYAMA, TAKAHIRO;TEZUKA, JUNICHI;REEL/FRAME:014729/0313;SIGNING DATES FROM 20031022 TO 20031106
Jan 10, 2006CCCertificate of correction
Sep 24, 2008FPAYFee payment
Year of fee payment: 4
Sep 12, 2012FPAYFee payment
Year of fee payment: 8